Process for the concentration of ores containing gold and uranium



PROCESS FOR THE CONCENTRATION OF ORES CONTAINING GOLD AND URANIUM Antoine M. Gaudin, N ewtonville, and John Dasher, Reading, Mass, assignors to the United States of America as represented by the United States Atomic Energy Com mission I No Drawing. Application January 26, 1949 Serial No. 73,003

7 Claims. c1. 23-145 This invention relates to an ore concentration process and more particularly to a flotation process for jointly concentrating the gold and uranium values from low grade ores containing both gold and uranium but substantially devoid of other valuable mineral constituents in sufiicient amounts to be of economic value.

The ores to which this invention is applicable are all mineralogically similar being composed of quartz pebbles surrounded by a quartzitic matrix in which the valuable minerals occur. The ores typically contain about 10 percent of foliated silicate minerals, which may be either sericite or pyrophyllite or both. In addition they contain pyrite, Uraninite, carbonaceous material, gold, and very small quantities of heavy minerals such as ilmenite, rutile, chromite, magnetite, zircon, and tourmaline. The pyrite content of these ores varies from about 1 percent to about 3 percent. The pyrite is rich in gold, but does not have.

much uraninite associated with it. The carbonaceous material in these ores is a hydrocarbon mineral. It is rich in both gold and uraninite and is recovered almost completely in the flotation operation. This hydrocarbon mineral is of low specific gravity and fragile, so it tends to concentrate in the slimes. Uraninite occurs as inclusions within the carbonaceous material. Uraninite is the only uranium mineral of importance in these ores. It occurs free and as locked particles with the other mineral constituents of the ores, especially hydrocarbon.

The gold content of these ores may vary from about 0.005 oz. to about 3.4 oz. per ton. The U content of these ores may vary from about 0.001% to about, 0.17%. It may therefore be seen that these ores are nothigh grade gold or uranium ores.

It is an object of the present invention to provide a method of concentrating the gold and uranium values of the above described ores while rejecting the quartz gangue associated therewith. Afurther object is to provide a concentrate of the gold and'uranium values of said ores from which the gold and uranium may be separately recovered by appropriate leaching operations. A still further object is to provide an appropriate flotation process for jointlyconcentrating the gold and uranium values of the above described ores. Other objects will appear hereinafter.

These objects are accomplished in accordance with the present invention by subjecting ores 'ofthe type described above to a flotation process wherein a fatty acid collector and a frothing agent are employed to secure a concentrate which contains the greater-portion of the gold and uranium values of the ore and a tailing which consists for the most part of the quartz gangue of the ore. It is usually considered good practice to employ a Xanthate collector along with the fatty acid collector' in order to make sure that a good recovery of both gold and uranium is obtained.

The-following examples illustrate but invention.

In the examples which, follow the groundore was diluted with water until the ore pulp contained from 20 do not limit the v2 a to 25% of solids before any flotation of the ore was attempted; 1 I

V 7 Example 1 A gold and uranium containing ore of the type described above which assayed 2.77, ounces of gold per ton and? contained 0.157% of U 0 was wet ground for an hour with half its Weight of water to reduce theore to a degree of fineness such that it could all pass thru a .100 mesh and flotation was again carried on for 30 seconds. Finally" the ore. was conditioned with 0.05 lb. of pine" oil per ton, and the final flotation operation was carriedout for 5% minutes. As a result of these operations a flotation concentrate was obtained which contained 22.9% of the solids, 83.3% of the uraniumvvalues and 98.9% of the gold Values that were present in the original etc. This concentrate analyzed 11.94 oz. of gold per ton and con The tailing contained 77.1%. of the solids of the ore, 16.7% of .the uranium values,

1.1% of the gold values, and assayed 0.04 oz. of gold' tained 0.57% of U 0 per ton and 0.034% in U 0 Example 2 A gold and uranium tained 0.0247% of U 0 was wet ground for an hour with half its weight of water to reduce the ore to a degree of Y fineness such that it could all pass thru a mesh screen." The ground ore was conditioned for 5 minuteswith 0.1

lb. of sodium oleate and' 0.1 lb. of sodium lignin sulphonate (Daxad #23) per ton of ore. Then 0.9 lb. of oleic acid per ton of ore was added, and the ore pulp was further conditioned for 10 minutes. Flotation was then carried on for 6 minutes. The ore was then con;

ditioned with 0.1 lb. per ton of potassium amyl xanth'ate v for 30 seconds, and further conditioned with 0.05 lb.

per ton of pine oil for 30'seconds. Flotation was then carried on for 8 minutes. As a result of these operations,

a concentrate was obtained which contained 21.2% of the -solids,'75.7% of the uranium values and 97.8% of the This concentrate analyzed 4.14 oz. of gold per ton and con-i The tailing contained 78.8%' of the solids, 24.3% of the uranium values and 2.2% of the gold values of the original ore, and assayed 0.007 oz. 1

gold values that were present in the original ore.

tained 0.088% of U 0 of gold per ton and 0.0071% in U 0 Example 3 A' gold and uranium containing ore of the type described above which assayed 3.22 oz. of gold per ton and contained 0.177% of U 0 was processed in accordance with j the directions given above in Example 1 except that no sodium lignin sulphonate was added to the ore pulp- Theflotation operations resulted in a concentrate that contained 19.8% of the solids, 84% of the uranium values and 99% of the gold values that were present in the 0 original ore. This concentrate analyzed 16.1102. ofgold per ton and contained 0.75% of U 0 The tailing whichwas obtained contained 80.2% of the solids, 16% of the uranium values and 1%, of the gold values of the original ore, and assayed 0.041 oz. of gold per'ton and 0.035%;

in U308.

Example 4 A gold and uranium containing ore of the type de- The ore was then conditioned for 30" containing ore of the type described above which assayed 0.883 oz. of gold per ton and con-"- 2,838,369 7 a r P scribed abovewhich assayed 3.11 oz. of gold per ton and contained 0.176% of U was processed in accordance with the directions given above in Example 1 except that no potassium amyl xanthate was added to the ore pulp. The. flotation operations resulted in a concentrate that contained 19.4% of the solids, 82.9% of the uranium values and 98.8% of the gold values that were present in the original ore. This concentrate analyzed 15.83 oz. of gold per ton and contained 0.75% of U 0 The tailing which was obtained contained 80.6% of the solids, 17.1% of the uranium values and 1.2% of the gold values of the original ore, and assayed 0.046 oz. of gold per ton and 0.037% in U 0 Example 5 A gold and uranium containing ore of the type described above which assayed 0.806 oz. of gold per ton and contained 0.026% of U 0 was wet ground for an hour With'h'alf its weight of water to reduce the ore to a degree of fineness such that it could all pass thru a 100 mesh screen. The ground ore was conditioned for 5 minutes with 0.1 lb. per ton of sodium oleate and then further cond-itioned for 15 minutes with 2.5 lb. per ton of oleic acid. There was then added to the ore 0.05 lb. per ton of potassium amyl xanthate and 0.03 lb. per ton of pine oil, and flotation was carried out in the rougher cell of the flotation machine for minutes. The concentrate thus obtained was treated without addition of further reagents in the cleaner cell of the flotation machine for 5 minutes. As a result of these operations there was obtained a cleaner concentrate which contained 17% of the solids, 78.2% of the uranium values and 98.2% of the gold values of the original ore. This cleaner concentrate analyzed 4.66 oz. of gold per ton and contained 0.12% of U 0 The cleaner tailing contained 10.3% of the solids, 5.4% of the uranium values and 1.2% of the gold values of the originalore, and assayed 0.09 oz. of gold per ton and 0.014% in U 0 The rougher tailing contained 72.7% of the solids, 16.4% of the uranium values and 0.6% of the gold values of the original ore, and assayed 0.007 oz. of gold per ton and 0.006l% in U 0 Example 6 .A gold and uranium containing ore of. the type described above which assayed 3.28 oz. of gold per ton and contained 0.182% of U 0 was wet ground for an hour with half its weight of water which reduced it to such a. state of fineness that 98% of it was minus 200 mesh. The ground ore was then'conditioned for 20 minutes with 2 lb. per ton of lndusoil, a refined tall oil containing a technicalmixture of fatty acids which is described on page 361 of the 3rd edition of The Condensed Chemical Dictionary (New York, 1942). Then flotation was carried on for 2 /2 minutes. The ore was then conditioned for 30 seconds with 0.05 lb. per ton of pine oil, and flotation was then carried on for 3 /2 minutes. As a result of these operations a flotation concentrate was obtained which contained 24.4% of the solids, 87.8% of the uranium values and 99.1% of the gold values of the original ore. This concentrate analyzed 13.31 oz. of gold per ton and contained 0.65% of U 0 The tailing contained 75.6% of the solids, 12.2% of the uranium values and 0.9% of the gold values of the original ore, and assayed 0.04 oz. of gold per ton and 0.029% in U 0 The gold values were removed from the concentrate by cyaniding. The solid concentrate was treated for 24 hours with four times its weight of a cyanide solution containing in a ton of solution 1 pound of NaCN and 1 pound of Ca'O. The solution from this cyaniding operation contained 98.5% of the gold values of the ore treated and no uranium. The residue left after the re moval of the cyanide leach solution contained only 0.6% of the gold values of the original ore. The residue from the cyanide leaching operation was then leached with a mineral acid such as nitric or sulfuric to extract the ma 4 ni-um values therefrom. For instance, the residual solids left from the cyanide leaching operation may be diluted with an equal weight of water to which 30 pounds per ton of sulfuric acid has "been added.

Example 7 A gold and uranium containing ore of the type described above which assayed 0.8-66 ounce of gold per ton and contained 0.0249%. of U 0 was wet ground for 30 minutes with half its weight of water to reduce the ore to minus 100 mesh. The ground ore was then conditioned in the flotation cell 0115 minutes with 0.5 lb. of sodium -oleateand 0.5 lb. of sodium lignin sulphonate per ton of ore. It was then further conditioned for 10 minutes with 1.5 lb. of oleic acid per ton. After then being conditioned with 0.2 lb. of sulphuric acid per ton, flotation was carried on for 4.25 minutes. The ore was then conditioned for 30 seconds with 0.1 lb. per ton of potassium arnyl xanthate and for 30 more seconds with 0.04 lb. per ton of cresylic acid. Flotation was then carried on for 5.75 minutes. As a result of these operations a flotation concentrate was obtained which contained 29.8% of the solids, 82.5% of the uranium values and 98.8% of the gold values that were present in the original ore. This concentrate analyzed 2.87 oz. of gold per ton and contained 0.069% of U 0 The tailing contained 70.2% of the solids of the ore, 17.5% of the uranium values, 1.2% of the gold values, and assayed 0.015 oz. of gold per ton and 0.0062% in U303- Example 8 A gold and uranium containing ore of the type described above which assayed 0.958 ounce of gold per ton and contained 0.0305 of U 0 was wet ground for an hour with half its weight of water to reduce the ore to minus 100 mesh. The ground ore was then conditioned for 20 minutes with 2 lbs. per ton of Indusoilff Flotation was then carried on 'for 7.25 minutes. The ore was then conditioned for 30 seconds with 0.04 lb, per ton of cresylic acid and flotation was carried on for 3.5 minutes.

As a result of these operations a flotation concentrate was obtained which contained 35.4% of the solids, 81.2% of the uranium values and 99% of the gold values that were present in the original ore sample. This concentrate analyzed 2.68 oz. of gold per ton and contained 0.07% of U 0 The tailing contained 64.6% of the solids of the 'ore, 1 8.8% of the uranium values, and 1% of the gold values, and assayed 0.015 oz. of gold per ton and 0.0089% 1 1 in U30 As a result of the flotation operations described in the above examples not only is the greater part of the gold and uraninite in the ore floated, but the greater part of the carbonaceous material, the pyrophyllite and the pyrite contained in the ore is also floated. Locked particles of sulfides and gold, sulfides and uraninite, carbonaceous material and uraninite, and foliated silicates and uraninite are also floated under the conditions set forth in the above examples with the result that excellent recoveries of both gold and uranium can be achieved.

Before the ore is subjected to flotation it must be ground to the required degree of fineness. The degree of fineness should be such as will reasonably unlock the various mineral constituents of the ore and such as will not leave more than the minimum of the ore too coarse to be lifted by flotation nor make much of the ore so fine that it will not properly respond to the flotation agents. A grind of ore fine enough to all pass mesh is generally satisfactory. Much of the flotation work pertaining to this invention has been carried out on pulps ground to about 98 percent minus 200 mesh, but it is not necessary to grind this fine to get good flotation of the uranium minerals. This fine grind was used because of the excellent gold recoveries which can thus be obtained. Uranium recovery has been found to be as good in pulps ground to 55 percent minus 200 mesh as in those ground to 98 percent minus 200' mesh. The finer the grind the better the gold recovery; hence, the desired gold recovery determinesthe fineness of grind. Uranium recovery is good at any reasonably fine grind.

Of the various reagents employed in the flotation work of the present invention, the best results were obtained using a simple combination of oleic acid, xanthate, and pine oil. While best results were obtained using technical grade oleic acid, nearly as good results have been obtained with the use of Indusoil, which is mentioned above in Example 6, and with the commercial grades of oleic acid designated as red oils. A crude fatty acid mixture known as Liqro, which is described on page 401 of the third edition of The Condensed Chemical Dictionary (New York, 1942) may also be used in place of technical grade oleic acid.

The quantity of fatty acid 'to be used varies with the composition of the ore. From about 1 pound to about 3 pounds of fatty acid per tonof ore is generally employed. The results are generally somewhat more consistent when more than the minimum amount of a fatty acid is used.

While oleic acid is the preferred fatty acid collector for use in the present invention, other fatty acids such as heptylic, pelargonic, lauric, cocoanut oil fatty acids, myris tic, palmitic, castor oil fatty acids and soya bean oil fatty acids may be used in place of oleic acid. It is advantageous to use a soap, such as sodium oleate, along with the fatty acid collector in order to improve the dispersion of the collector. I e

The potassium amyl xanthate used in the flotations was generally derived from the technical mixture of isomeric amyl alcohols known as pentasol. Pentasol is described in detail on page 350 of the 2nd edition of The Condensed Chemical Dictionary (New York, 1930). The xanthate reagent has been used in amounts ranging from 0.025 pound up to 0.1 pound per ton of ore. The xanthate reagent helps to recover pyrite, some of which is diflicult to float, and thereby helps to float some of the gold.

While potassium amyl xanthate is the preferred xanthate reagent used in the flotations of the present invention, alkali metal salts of other alkyl xanthates may be used such as the alkali metal salts of ethyl xanthate, isopropyl xanthate, butyl xanthate, hexyl xanthate, and cetyl xanthate.

Enough frother should be used to get a good froth, but care should be taken to not use too much frother'in the presence of a fatty acid collector or activated quartz will be floated. It was found that from 0.01 to 0.05 pound of pine oil per ton of ore was enough to give good results. Oleic acid produces a tough, voluminous froth of itself, and this can be modified and improved by the addition of a small quantity of pine oil. High gold recovery is dependent upon keeping a good stable froth in the'cell. Pine oil, the most common frother, was used in most of the Work on this invention and gave satisfactory results. It has been found, however, that other well known frothers are substantially as eflicacious as pine oil. Other frothers which have been successfully used in the present invention include cresylic acid, tributyl amine, mixtures of pine oil with kerosene, amyl alcohol, methyl isobutyl carbinol, and the complex mixture of branched, open chain, aliphatic alcohols containing six or more carbon atoms which are obtained as byproducts in the catalytic synthesis of methanol from carbon monoxideand hydrogen.

The sodium lignin sulphonate used as a modifier in some of the above examples increases the selectivity of the flotation of uranium mineral from quartz gangue. Sodium silicate, tetrasodium pyrophosphate, oxalic acid, tartaric acid, and quebracho may also be used in place of sodium lignin sulphonate to increase the selectivity of the float for uranium mineral.

If it is desired to improve the recovery of gold in the flotation process this can be done by using from 0.5 to 5 pounds per ton of ore of a hydrocarbon extender along with the fatty acid col-lecton Among suitable hydrocarlbon extenders are kerosene, fuel oil, gas oil, white oil for fatty acid flotations.

and crude petroleum oil. While the use of these hydrocan bon extenders improves the gold recovery it has adeleterious effect on the flotation of uranium values; therefore hydrocarbon extenders are not used in the flotation ifhig'h recovery of uranium values is desired.

It has been found that oleic acid tends to float activated quartz rather easily, but if the pulp is conditioned with oleic acid for a minimum of ten minutes before a froth is removed, the float is more selective and much less of the quartz floats. If desired, the pulp may be conditioned with all of the flotation reagents together beforeany flotation of the ore 'is attempted. The'additionof a; soap to the ore pulp .before the fatty acid collectoris added thereto appears to be advantageous. Since too much frothing promotes the flotation of quartz and since this is 'not desired, some of thesteps in flotation are designed to minimize frothing. The oleic acid conditioning period is one, of these. Another is the practice of adding pine oil only after the bulk of the float is finished and the froth-has begun to die. If pine oil is added at this stage, the last bit ofpyrophyllite and pyrite float without at the same'timefloating' too much quartz. y V

Flotation time for the oleic acid float is about normal In some of the better tests the roughing operation was carried on for ten minutes and the rougher froth cleaned for five minutes. The longer the flotation time, the better the recovery of both uranium and gold. As long as any froth remains to be collected it is worth while collecting it. In other words, the rougher float should in practice he followed by a scavenging float.

In the batch tests the froth'dies after about ten minutes so froth can no longer be collected. In an operating bank of cells this could be mitigatedyby using froth crowde'rs in V the scavenging cells.

The oleic acid float'does not'workwell if'the pH of the pulp is'either too high or too. low. Ata pH above about 8 a voluminous sudsy froth becomes prominent, and good selective flotation becomes practically impossible. At a pH below about 5 the froth tends to be flat and fragile. Good results were obtained at pH values between 6 and 7.5 with most of the best runs at about pH 7.5. 7

Water is an important item for the fatty acid flotations of the present invention. In general, hard'water will consume oleic acid. The calcium and magnesium in the water react with oleic acid to form insoluble'calcium and magnesium oleates, which are poor flotation reagents. Calcium and magnesium ions also tend to activate quartz for oleic acid flotation. The flotation process of the present invention is usually facilitated and.

the results are usually improved if water is used in which the content of cations capable of forming insoluble soaps is kept at a. sufliciently low concentration. Thus it is desirable to have water of high chemical quality. It has been found advantageous to add to the flotation liquor small quantities of certain chemicals that sequester the calcium and magnesium ions present in hard water. Examples of such sequestering agents are sodium phosphate, sodium silicate and lignin sulfonates. When the quality of water is very hard it can be softened by the lime-soda process. Moderately hard waters can be suitably softened by ion exchange methods utilizing such materials as synthetic ion exchange resins or natural zeolites. One advantage of the flotation process of the present invention is that it gives a small weight of flotation concentrategenerally about one-fifth of the weight of the ore treated-that can be acid leached for uranium and leached with cyanide for gold at a comparatively lowcost because only one-fifth the weight of material needs to be handled thus reducing the leaching costs compared with the expense Qfleaching the whole ore. .Furthermore, the flotation concentrate is comparatively highgrade in uranium, and this results in the final precipitate from uranium leaching being higher grade than if it 7 came from a leach of the whole ore. The advantage of this flotation process in relation to gold recovery is "that only a small percentage ofthe ore has to be cyanided; In addition, this smaller amount may be reground to give improved gold recovery. As can be seen from the above examples, very little gold is left in the flotation tailings. Resort maybe had to such modifications and variations as fall within the spirit of the invention and the scope of the appended claims.

We claim:

l 1. A process of jointly concentrating the gold and uranium values from a low grade gold and uranium bearing ore which contains large amounts of-quartz gan'gue and also some foliated silicate minerals, pyrite and carbonaceous material which comprises subjecting the ore to a froth flotation process ata pH between 5 and 8 employing a fatty acid collector, a supplementary xanthate collector and a frothing agent.

2. A process as defined in claim 1 wherein softened water'is used in the flotation process.

3. A process of jointly concentrating the gold and uranium values from a low grade gold :and uranium bearing ore which contains large amounts of quartz gangue and also some foliated silicate minerals, pyrite and carbonaceous material which comprises subjecting an aqueous pulp of the ground ore at a pH between ,6 and 7.5 to froth flotation using oleic acid and potassium amyl xanthate as collectors and pineoil as a frother.

4. A process as recited in claim 3 wherein the flotation concentrate is subsequently leached with a cyanide solution to remove gold values therefrom and then acid leached to remove uranium values therefrom.

5. A process of jointly concentrating the gold and uranium values from a low grade gold and uranium bearing ore which contains large amounts of quartz gangue and also some foliated silicate minerals, pyrite and carbonaceous material which comprises grinding the ore to an appropriate state of fineness, conditioning an aqueous pulp of the ore for at least ten minutes with oleic acid at a pH between '5 and 8, then carrying on flotation for several minutes, conditioning theaqueousore ore to an appropriate state of fineness, adding, ,a .soap

and sodium lignin sulphonat'e'to an aqueous pulp .of the ground ore, conditioning said aqueous ore pulp'fo'r at least 10 minutes with ,oleic acid at a pH between 5 and 8, then carrying on flotation for several minutes, conditioning said aqueous ore pulp with potassium amyl xanthate and pine oil, and then carrying on flotation again for several minutes.

References Cited in the file of this patent UNITED STATES PATENTS 1,070,313 Adams -Aug. 12, 1913 2,000,656 Armstrong et al. May 7, 1935 2,185,591 Jayne Jan. -2, 1940 2,251,217 Woodhouse July 29, 1941 OTHER REFERENCES Large: Engineering and Mining Journal, vol; 136, No. 3 Pp. 116118 (1935).

Thorpe: Dictionary of Applied Chemistry, 4th 'ed., vol. 3, p. 464 (1939). 

1. A PROCESS OF JOINTLY CONCENTRATING THE GOLD AND URANIUM VALUES FROM A LOW GRADE GOLD AND URANIUM BEARING ORE WHICH CONTAINS LARGE AMOUNTS OF QUARTZ GANGUE AND ALSO SOME FOLIATED SILICATE MINERALS, PYRITE AND CARBONACEOUS MATERIAL WHICH COMPRISES SUBJECTING THE ORE TO A FROTH FLOTATION PROCESS AT A PH BETWEEN 5 AND 8 EMPLOYING A FATTY ACID COLLECTOR, A SUPPLEMENTARY XANTHATE COLLECTOR AND A FROTHING AGENT. 